WASHINGTON (Reuters) - Federal prosecutors in Detroit on Thursday unsealed charges against former Volkswagen Chief Executive Martin Winterkorn, accusing him of conspiring to mislead regulators about the German automaker’s diesel emissions cheating.

Volkswagen did not immediately comment

An indictment filed in secret in March was unsealed in U.S. District Court on the same day as Volkswagen’s annual meeting in Germany. Winterkorn resigned soon after the scandal over polluting vehicles in the United States became public in September 2015.

U.S. Attorney General Jeff Sessions said in a statement that the charges show “Volkswagen’s scheme to cheat its legal requirements went all the way to the top of the company.”

Winterkorn is charged with conspiracy to defraud the United States, wire fraud and violating the Clean Air Act from at least May 2006 through November 2015 by using illicit software that allowed Volkswagen diesel vehicles to emit excess pollution without detection.

Volkswagen initially suggested that only lower level executives knew of the cheating. But the indictment alleges Winterkorn was informed of VW’s diesel emissions cheating in May 2014 and in July 2015 and he agreed with other senior VW executives “to continue to perpetrate the fraud and deceive U.S. regulators,” prosecutors said.

A spokeswoman for the U.S. Attorney’s office in Detroit said Winterkorn was not in custody. In total, nine people have been charged and two have pleaded guilty in the case. One Italian citizen, a former Audi manager, is in Germany awaiting extradition.

Six of the former Volkswagen executives charged are in Germany and have avoided facing U.S. prosecutors because Germany typically does not extradite its citizens.

(Reporting by David Shepardson; editing by Grant McCool and Dan Grebler)